This invention relates in general to an improved measuring device which is suitable for use as an indicator in a comparator test set. More particularly, the measuring device of the present invention is comprised of a parallel suspension reed type of measuring device wherein the weight of its moving components is effectively eliminated to thereby improve the accuracy of the measurements made by the device. By maintaining the moving components of the device in a weightless condition, these components are insulated from outside forces and disturbances to thereby ensure that the accuracy of this device is not affected by external factors such as position, gravity, temperature, etc.
Accurate measurement represents one of the most critical aspects of industrial inspection and production. Because a measurement is only as precise as the instrument used in making it, all measuring devices and particularly those used by industry should be extremely reliable in terms of accuracy and repeatability. In other words, it is highly desirable for a measuring device which is frequently used by industry to be capable of repeatedly providing accurate measurements. Another desirable feature of any measuring device is that it exhibit a short lag time between start and readout of the measurement. Finally, it is extremely important for a measuring device to be easy to use and capable of producing high amplification of the measured quantity without appreciable distortion of the measurement.
A reed measuring device represents a presently known measuring device which exhibits many of these characteristics. A reed measuring device is comprised of a pair of blocks which are positioned adjacent to each other and are joined together by a pair of parallel reed suspension springs. One of the blocks is rigidly fixed while the other block is free to move relative to the stationary block. The movable block has a measuring spindle connected to its bottom and a vertical reed attached to the inside top part of the block. A second vertical reed is similarly attached to the inside top part of the stationary block. The two vertical reeds are then connected to each other at their upper ends and a pointer is attached to them at this point. During the gauging or measuring operation, the gauging spindle is brought in contact with the piece to be measured causing the movable block to be moved upward in response to the measured dimension of the piece. This upward movement of the movable block causes the vertical reed attached to this block to slip past the vertical reed attached to the stationary block. Since these reeds are joined at their upper ends, movement of one reed past the other reed is prevented causing both of the reeds to swing through an arc which is representative of the measured quantity. The pointer moves in unison with these reeds to mechanically amplify the measured quantity. This arcuate movement of the pointer is then converted into a reading suitable for display.
Since this measuring device employs no gears, bearing surfaces or rubbing contacts, friction and surface wear between the movable components of this device are entirely eliminated. As a result, this measuring device is extremely reliable when properly used. This device, however, possesses an inherent disadvantage which is common to all fulcrum and lever type of measuring devices. In particular, the weight of the moving components can and do have a significant impact upon the operation of the device if the device is not used in a truly vertical position. If the measuring device is improperly positioned, the weight of the floating block is not properly carried by the reeds and the accuracy of the measurement is correspondingly affected. Accordingly, this type of measuring device is accurate only when it is used in a truly vertical position.
The measuring device of the present invention, however, overcomes this problem by maintaining its movable components in a weightless condition. In particular, the movable block is constructed to have a hollow inner cavity which is either evacuated or filled with a gas that increases the buoyancy of the block. The vertical reeds are in turn attached to each other by means of a buoyant joining piece which is also constructed to have a hollow inner cavity. The inner cavity of the buoyant joining piece is either evacuated or filled with a gas that increases the buoyancy of this piece. A hollow amplification arm is attached to the buoyant joining piece to mechanically amplify the arcuate movement imparted to this piece during a measurement. The hollow portion of the amplification arm is either evacuated or filled with a gass which increases the buoyancy of this component. The movable components are also encompassed by a fluid having a density which substantially reduces the weight of these components. Through proper selection of the gas used to fill the hollow cavity in the movable block, the buoyant joining piece and the amplification arm and the fluid used to encompass these components, the movable components of the device are maintained in a weightless condition.
By maintaining the movable components in a weightless condition, the parallel reed suspension springs are only used to provide gauging pressure and to align the movable components of the device. Since the parallel reed suspension springs do not have to support the weight of the movable components, the measuring device of the present invention may be used in any position without a detrimental effect upon the accuracy of the measurements made by the device. In addition, the parallel reed suspension springs and vertical reeds can now be made to have a thinner more flexible nature. As a result of this type of construction, the measuring device of the present invention is capable of providing high amplification while still exhibiting low gauging pressure. Another advantage of this measuring device is that it is capable of providing greater amplification of the quantity being measured. The degree of amplification is established by the length of the flexible portion of the vertical reeds divided by the distance between the center line of these reeds plus the length of the amplification arm. By making the vertical reeds thinner, the center line of these reeds can be positioned closer together to thereby increase the degree of amplification while reducing the size of the device. As a result, the measuring device of the present invention is more compact, easier to use, and less expensive than the reed measuring devices which are presently available.
The measuring device of the present invention exhibits the added feature of providing improved magnification of the amplified measurement for readout. In the preferred embodiment of the invention, a target is attached to the amplification arm for movement in combination therewith. This target is comprised of a transparent material having a curved shape and a graduated face. The face of the target is then magnified by means of a lens system which is comprised of an objective lens positioned near the target and an occular lens appropriately positioned with respect to the objective lens. By properly arranging the distance between these lenses, they operate as an inverted microscope to provide an enlarged image of at least a portion of the target. The image of the target is then focused through an eye piece for projection onto a screen comprising ground glass or a similar type of material for easier readout of the magnified measurement. The screen has a reference line etched on it to provide a reference point from which readings may be made. This type of lens system allows for the measuring device to be capable of being made more compact and greatly extends the useful range of the instrument by eliminating the need for a long light path or complex electrical circuitry.
It is therefore an object of the present invention to provide a measuring device wherein the device's movable components are maintained in a weightless condition to improve the accuracy of the device.
Another object of the present invention is to provide an improved measuring device of the character described which is capable of providing extremely accurate measurements regardless of the position of the device.
Another object of the present invention is to provide an improved measuring device of the character described which is capable of accurately amplifying the measured quantity.
A further object of the present invention is to provide an improved measuring device of the character described which includes an inherent dampening effect which significantly decreases lag time between the start of the measurement and readout of the measured quantity.
An additional object of the present invention is to provide a measuring device of the character described which is capable of providing high amplification while still exhibiting low gauging pressure.
Another object of the present invention is to provide a measuring device of the character described which is capable of producing a greater degree of amplification in a fairly compact device thereby making the device small in size, easy to use and low in cost.
An additional object of the present invention is to provide an improved measuring device of the character described which is capable of providing accurate measurements which are not effected external factors such as position, gravity, temperature, etc.
It is another object of the present invention to provide an improved measuring device of the character described which is capable of magnifying the amplified measurement to facilitate readout of the measured quantity.
It is a further object of the present invention to provide an improved measuring device of the character described which is capable of being incorporated into a hand tool.
Other and further objects of this invention, together with the features of novelty appurtenant thereto, will appear in the course of the following description.